1. Cross-reference to related applications
This application is related to copending application U.S. Ser. No. 691,768, filed Jan. 16, 1985, which is directed to a process for applying a thin, clear antistatic layer to a photographic film. The present invention provides an auxiliary layer designed to be coated over such layer.
2. Field of the Invention
This invention is in the field of photographic film. More particularly, this invention is directed to backing layers for such film which can conduct antistatic properties from an antistatic underlayer to the outside surface the backing.
3. Background Art
Polymeric film supports for photographic film are known for their propensity to accumulate static charges. This is a particular problem where the film is designed to be handled by machine and to be processed rapidly over unlike surfaces. Static charges which may be generated at this time cannot be readily tolerated because discharging these may expose the photographic layer, or layers, coated thereon.
The use of so-called antistatic layers to prevent the build-up of these static charges is well known in the art. Schadt patent, U.S. Pat. No. 4,225,665, describes one such composition comprising a mixture of (1) a water-soluble copolymer of the sodium salt of styrene sulfonic acid and a carboxyl-containing monomer, (2) a hydrophobic polymer containing carboxyl groups, and (3) a water-soluble polyfunctional aziridine. When this mixture is applied as a single layer to resin-subbed (resin-subcoated) poly(ethylene terephthalate), for example, it provides excellent protection from the build-up of static charges (e.g. surface resistivity).
Copending application U.S. Ser. No. 691,768, filed Jan. 16, 1985 describes an improvement over the Schadt patent wherein component (1) is applied to the support in a first coating, optionally a composition containing component (2), and component (3) is applied as a second coating contiguous thereto. This improved process permits the application of thinner layers without premature reaction of the aziridine with the other ingredients. Products from such premature reaction can sometimes plug and foul coating equipment, which is not commercially tolerable.
Nevertheless a problem with prior art antistatic layers generally is that coatings applied thereto tend to mask or cover their antistatic properties. The present invention provides a solution to that problem.